Single evaporator refrigerator/freezer unit with interdependent temperature control

ABSTRACT

A combination refrigerator/freezer unit with an insulated cabinet defining a refrigerator section, a freezer section and at least one air passage between the freezer section and refrigerator section. A single evaporator is disposed in the freezer section. A controller controls operation of the refrigeration system. The controller receives input signals from freezer and refrigerator sensors and controls the refrigeration system to pass refrigerant to the evaporator in the freezer section according to at least one temperature parameter of the refrigerator section sensed by the refrigerator sensor.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit of U.S. Provisional patent application Ser. No. 60/862,376 filed on Oct. 20, 2006, and entitled “Cooling Unit,” hereby incorporated by reference as if fully set forth herein.

STATEMENT OF FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to refrigerated food and drink units, and in particular, a controller for controlling the temperature of a cooling unit.

2. Description of the Related Art

Refrigerators and coolers for the cold storage of food and beverage items are well known. Some cooling units include a freezer section and a refrigerator section. Typically, the freezer section is cooled by a refrigeration system. The refrigeration system includes a compressor, a condenser, an expansion device, and an evaporator connected in series and charged with a refrigerant. The evaporator is a specific type of heat exchanger that transfers heat from air passing over the evaporator to refrigerant flowing through the evaporator, thereby causing the refrigerant to vaporize. The cooled air is then used to refrigerate the freezer section.

An air passage between the freezer section and the refrigerator section allows chilled air from the freezer section to cool the air in the refrigerator section. Thus, the refrigerator section is cooled when the freezer section is cooled and the refrigerator section is not cooled by a separate evaporator.

The refrigerator section temperature is related to the temperature of the freezer section. For example, the temperature of the freezer section can be approximately a number of degrees less than the refrigerator section temperature. A controller can control the refrigeration system based only on the temperature of the freezer section because the refrigerator section temperature is related to the freezer section temperature. A thermostat mounted in the freezer section can control the refrigeration of a cooling unit. Additionally, a controller connected to a temperature sensor in the freezer section can be programmed with a freezer section set point and run the refrigeration system to keep the freezer section around the freezer section set point. This will also maintain the refrigerator section within a range of temperatures.

The temperature control of the freezer section is performed without concern for the actual temperature of the refrigerator section. The freezer section temperature can be allowed to vary more than the refrigerator section temperature because the freezer section temperature is usually always below freezing and, thus, the food product will remain frozen. The food product stored in the refrigerator section needs to be cooled to a narrow temperature range because of food safety and the need to prevent freezing in the refrigerator section.

Freezing temperatures in the refrigerator section can be problematic when the refrigerator section is colder than expected due to abnormal ambient air temperatures, defrost problems, or variations in the food product stored in the cooling unit. The controller is properly controlling the temperature of the freezer section, but the relationship between the freezer section temperature and the refrigerator section has changed and the controller is no longer able to adequately control the temperature in the refrigerator section. This can mean that the normal freezer section temperature will cause the refrigerator section to be too cold and can even cause freezing in the refrigerator section that causes damage to the food product stored therein.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a combination refrigerator/freezer unit with an insulated cabinet defining a refrigerator section, a freezer section and at least one air passage between the freezer section and refrigerator section. A freezer sensor can be disposed in the freezer section and can sense a freezer section temperature. A refrigerator sensor can be disposed in the refrigerator section and can sense a refrigerator section temperature. The unit can include a refrigeration system having a single evaporator disposed in the freezer section. A controller can control operation of the refrigeration system by receiving input signals from the freezer and refrigerator sensors and control the refrigeration system to pass refrigerant to the evaporator in the freezer section according to at least one temperature parameter of the refrigerator section sensed by the refrigerator sensor.

One temperature parameter can be a refrigerator section minimum temperature, and the controller can be configured to prevent the refrigerator section temperature from dropping below the refrigerator section minimum temperature.

The controller can be programmed with a freezer section set point, and the controller can be configured to energize the refrigeration system when the freezer section temperature is above the freezer section set point.

Another temperature parameter can be a refrigerator section set point and the controller can be configured to energize the refrigeration system when the refrigerator section temperature is above the refrigerator section set point.

The controller can be configured to run the refrigeration system until the freezer section temperature is below the freezer section set point, and the refrigerator section temperature is below the refrigerator section set point.

The controller can be programmed with a freezer section set point offset and the controller can be configured to shut off the refrigeration system when the freezer section temperature reaches the freezer section set point minus the freezer section set point offset and the refrigerator section temperature is below the refrigerator section set point.

Another temperature parameter can be a refrigerator section set point offset, and the controller can be programmed with a freezer section set point offset. The controller can be configured to shut off the refrigeration system when the refrigerator section temperature reaches the refrigerator section set point minus the refrigerator section set point offset after the controller detected and even when the refrigerator section temperature was not below the refrigerator section set point when the freezer section temperature reached the freezer section set point minus the freezer section set point offset.

The combination refrigerator/freezer unit can include a user input connected to the controller and the temperature parameters can be set by the user input. The freezer section can equal the refrigerator section set point minus a temperature set point difference.

Another aspect of the invention provides a combination refrigerator/freezer unit with an insulated cabinet defining a refrigerator section, a freezer section and at least one air passage between the freezer section and refrigerator section. A freezer thermistor can be disposed in the freezer section and it can sense a freezer section temperature. A refrigerator thermistor can be disposed in the refrigerator section and it can sense a refrigerator section temperature. The combination refrigerator/freezer unit can include a refrigeration system having a single evaporator disposed in the freezer section. A controller can control operation of the refrigeration system and receive input signals from the freezer and refrigerator sensors. The controller can be programmed with a refrigerator section minimum temperature and a refrigerator section set point. The controller can be configured to control the refrigeration system to energize the refrigeration system when the refrigerator section temperature is above the refrigerator section set point. The controller can be configured to disable the refrigeration system when the refrigerator section temperature is less than the refrigerator section minimum temperature.

The controller can be programmed with a freezer section set point and the controller can be configured to energize the refrigeration system when the refrigerator section temperature is above the refrigerator section set point.

The controller can be configured to energize the refrigeration system until the refrigerator section temperature reaches the refrigerator section set point.

Another aspect of the present invention provides a method of controlling a combination refrigerator/freezer unit with an insulated cabinet defining a refrigerator section, a freezer section, at least one air passage between the freezer section and refrigerator section, and a refrigeration system having a single evaporator disposed in the freezer section. The method can include sensing a freezer section temperature with a refrigerator sensor, sensing a refrigerator section temperature with a freezer sensor, and controlling the refrigeration system to pass refrigerant to the evaporator in the freezer section according to at least one temperature parameter of the refrigerator section sensed by the refrigerator sensor.

One temperature parameter can be a refrigerator section minimum temperature and the refrigerator section temperature can be prevented from dropping below the refrigerator section minimum temperature.

The refrigeration system can be energized when the freezer section temperature is above a freezer section set point.

Another temperature parameter can be a refrigerator section set point and refrigeration system can be energized when the refrigerator section temperature is above the refrigerator section set point.

The refrigeration system can be energized until the freezer section temperature is below the freezer section set point and the refrigerator section temperature is below the refrigerator section set point.

Another temperature parameter can be a refrigerator section set point offset. The refrigeration system can be energized when the freezer section temperature reaches the freezer section set point plus a freezer section set point offset. The refrigeration system can be energized when the refrigerator section temperature reaches the refrigerator section set point plus the refrigerator section set point offset. The refrigeration system can be energized until the freezer section temperature reaches the freezer section set point minus the freezer section set point offset. The refrigeration system can be energized until the refrigerator section temperature reaches the refrigerator section set point.

The refrigeration system can be energized until the refrigerator section set point reaches the refrigerator section set point minus the refrigeration set point offset after an event when the freezer section temperature had reached the freezer section set point minus the freezer set point offset and the refrigerator section temperature had not reached the refrigerator section set point.

Various other features and advantages of the present invention will be made apparent from the following detailed description and the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a combination refrigerator/freezer unit having the features of the present invention;

FIG. 2 is a perspective view thereof similar to FIG. 1 albeit with its cabinet door open so that the interior of the cabinet is visible;

FIG. 3 is a front elevation view thereof with the cabinet door removed;

FIG. 4 is an exploded assembly view thereof;

FIG. 5 is a diagram of the refrigeration system of the combination unit;

FIG. 6 is a schematic of the electrical system of the combination unit; and

FIG. 7 is a flow chart illustrating the interdependent temperature control.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-4, in one preferred form, a combination refrigerator/freezer unit 30 includes a cabinet 32 defining a cavity with a forward opening 34 that is divided by horizontal and vertical partition walls 36 and 38, respectively, into a refrigerator section 40 and a freezer section 42. The refrigerator section 40 is an L-shaped chamber having a molded insert liner 44 with grooves that support shelves 46 (two are shown in the drawings). The shelves 46 are supported by corresponding grooves formed in the vertical partition wall 38. Molded insert liner 44 includes a pair of grooves that support a lower support shelf 48 and defines a recess for a crisper drawer 50. The freezer section 42 is a rectangular chamber having a foam insulated, molded insert 52 containing a cube ice maker assembly 54 and an ice storage bin 56. Alternatively, the freezer section 42 could include a freezer shelf (now shown) and be used to freeze food items as is known in the art. The freezer section 42 is closed by a door 58 that is hinged to insert 52 along one vertical side thereof. The cabinet opening 34 is closed by a door 60 that is hinged to the cabinet 32 (with self-closing cams) along one vertical side thereof. Both the cabinet 32 and the door 60 are formed of inner molded plastic members and outer formed metal members with the space between the members filled in with an insulating layer of foam material, all of which is well known in the art. The door 60 has a handle 61 and can include one or more door shelves.

Referring now to FIGS. 4 and 5, the unit 30 includes a refrigeration system 62. The refrigeration system 62 includes an evaporator 64 positioned along the back wall of the freezer section 42. The evaporator 64 has serpentine refrigerant tubes running through thin metal fins. With reference to FIG. 5, the evaporator 64 has an outlet line 68 which is connected to an inlet 71 of a compressor 70. A discharge line 72 connected to an outlet 73 of the compressor 70 is connected to the inlet of a condenser 74 having an outlet line 76 connected to a dryer 78. A capillary tube 80 leads from the dryer 78 an inlet line 82 of the evaporator 64. A bypass line 84 leads from the dryer 78 to the inlet line 82 of the evaporator. A hot gas bypass valve 86 controls communication between the dryer 78 and the evaporator 64. Bypass valve 86 can be an electronically controlled solenoid type valve. An evaporator fan 90 is positioned near the evaporator 64 and a condenser fan 92 is positioned near the condenser 74. An evaporator pan 94 is positioned beneath the evaporator 64 and is configured to collect and drain water. An evaporator pan heater 96 is beneath the evaporator pan 94 to heat the evaporator pan 94. The compressor 70, condenser 74 and condenser fan (see FIG. 13) are located at the bottom of the cabinet 32 below the insulated portion.

Referring now to FIGS. 3 and 6, a controller 128 is attached below the cabinet and adjacent a kickplate 130 positioned below the cabinet door 60. The controller 128 comprises a microprocessor (not shown) that is connected to a memory (not shown). Alternatively, the microprocessor can include a memory. A plurality of connectors and lines (not shown) connect the controller 128 to sensors (discussed below) and relays associated with the other electrical components (not shown) of the refrigeration unit 30.

A refrigerator section temperature sensor 138 is attached to refrigerator section 40 (see FIGS. 3 and 4) and senses the temperature of refrigerator section and provides refrigerator section temperature information to the controller 128. A freezer section temperature sensor 140 is attached to the freezer section 42 (see FIGS. 3 and 4) and senses the temperature of the freezer section 42 and provides freezer section temperature information to the controller 128. The temperature sensors 138 and 140 can comprise thermistors or other appropriate temperature sensors. The controller 128 is configured to control refrigeration, ice making, defrost and other aspects of the refrigeration unit 30 as will be described hereinafter.

As is known, the compressor 70 draws refrigerant from the evaporator 64 and discharges the refrigerant under increased pressure and temperature to the condenser 74. The hot, pre-condensed refrigerant gas entering the condenser 74 is cooled by air circulated by the condenser fan 92. As the temperature of the refrigerant drops under substantially constant pressure, the refrigerant in the condenser 74 liquefies. The smaller diameter capillary tube 80 maintains the high pressure in the condenser 74 and at the compressor outlet 73 while providing substantially reduced pressure in the evaporator 64. The substantially reduced pressure in the evaporator 64 results in a large temperature drop and subsequent absorption of heat by the evaporator 64. The evaporator fan 90 can draw air from inside the freezer section 42 across the evaporator 64, the cooled air returning to the freezer section 42 to cool the freezer section 42. At least one air passage (not shown) connects the freezer section 42 and the refrigerator section 40 so that the refrigerator section 40 is cooled by the freezer section 42, the temperature of the refrigerator section 40 is thus related to the temperature of the freezer section 42. In an embodiment, the temperature of refrigerator section 40 is 30 degrees Fahrenheit warmer than the temperature of the freezer section 42.

As mentioned, the refrigeration system includes a hot gas bypass valve 86 disposed in bypass line 84 between the dryer 78 and the evaporator inlet line 82. Hot gas bypass valve 86 is controlled by controller 128. The evaporator 64 is defrosted for a defrost time up to a maximum defrost time after a certain amount of compressor runtime. When the hot gas bypass valve 86 is opened, hot pre-condensed refrigerant will enter the evaporator 64, thereby heating the evaporator 64 and defrosting any ice buildup on the evaporator 64. The evaporator pan heater 96 heats the evaporator pan 94 when the hot gas bypass valve 86 is opened so that ice in the evaporator pan 94 is melted at the same time that the evaporator 64 is defrosted. The hot gas bypass valve 86 and evaporator pan heater 96 are controlled by the controller 128 (i.e., the defrost cycle is controlled by the controller 128).

Referring now to FIG. 3, a user interface control unit 160 is mounted to the top of the refrigerator molded insert liner 44 within the cabinet 32 for receiving user commands and forwarding input signals to the main controller 128. The control unit 160 includes a display panel 164 and a power input 168, a warmer input 170, a cooler input 172 and a light input 174. A refrigerator section set point can be set by the user through the control unit 160. A freezer section set point is based on the refrigerator section set point (e.g., freezer section set point is minus 30 degrees Fahrenheit of the refrigerator section set point). Alternatively, the freezer section set point could be set by the user.

The controller 128 uses fuzzy logic to cool the unit 30 by controlling the refrigeration system 62 based on the temperature of the freezer section 42 and the temperature of the refrigerator section 40. The controller 128 cools the freezer section 42 until it is cold enough and then checks to see if the refrigerator section 40 is cold enough. If the refrigerator section 40 is not cold enough, the controller 128 continues to cool the unit 30 until the refrigerator section 40 is cold enough even if the freezer section gets too cold. The controller 128 shuts off the refrigeration system 62 when both the freezer section 42 and the refrigerator section 40 are cold enough. The controller 128 turns on the refrigeration system 62 when the freezer section 42 or the refrigerator section 40 become too warm, the controller 128 then cooling the unit 30 until the freezer section 42 and the refrigerator section 40 are cold enough. The controller 128 always monitors whether the refrigerator section 40 is too cold and shuts off the refrigeration system 62 when the refrigerator section 40 is too cold.

The controller 128 runs refrigeration system 62 (i.e., energizes the compressor 70, condenser fan 92, and evaporator fan 90) until the temperature of the freezer section 42 is below the freezer section set point. Once the freezer section temperature is below the freezer section set point, the controller 128 stops the refrigeration system 62 if the temperature of the refrigerator section 40 is below the refrigerator section set point. If the temperature of the refrigerator section 40 is not below the refrigerator section set point when the set point of the freezer section 42 is met, the controller 128 continues to run the refrigeration system 62 until the temperature of the refrigerator section 40 is below the refrigerator section set point regardless of the temperature of the freezer section 42.

During any cooling cycle and regardless of the freezer section temperature, if the temperature of the refrigerator section 40 reaches a minimum refrigerator section temperature (e.g., 34 degrees Fahrenheit), the refrigeration system 62 is de-energized by the controller 128 to prevent the refrigerator section 40 from being cooled beyond the freezing point.

The controller 128 is programmed with a freezer section set point tolerance (e.g., five degrees Fahrenheit) for the freezer section temperature sensor 140 to smooth out the refrigeration system 62 on and off cycles at near the freezer section set point. This can achieve an average freezer section temperature equal to the freezer section set point. Likewise, the controller 128 is programmed with a refrigerator section set point tolerance (e.g., two degrees Fahrenheit) for the refrigerator section temperature sensor 138 to smooth out the refrigeration system 62 on and off cycles at near the refrigerator section set point. This can achieve an average refrigerator section temperature equal to the refrigerator section set point. The set point tolerances can also be set by a user to provider greater control.

For example, if the set point of the refrigerator section 40 is 38 degrees Fahrenheit, the set point of the freezer section 42 is 8 degrees Fahrenheit (i.e., refrigerator section set point minus thirty degrees). The controller 128 will run the refrigeration system 62 until the freezer section temperature is 3 degrees Fahrenheit (i.e., freezer section set point the five degree freezer section set point tolerance). If the refrigerator section temperature is below the refrigerator section set point (i.e., 38 degrees Fahrenheit) when the freezer section temperature reaches 3 degrees Fahrenheit, the controller 128 shuts off the refrigeration system 62. If the refrigerator section temperature is above the refrigerator section set point (i.e., 38 degrees Fahrenheit) when the freezer section temperature reaches 3 degrees Fahrenheit, the controller 128 will disregard the freezer section temperature and continue to run the refrigeration system 62 until the refrigerator section temperature reaches the refrigerator section set point minus the refrigerator section set point tolerance (i.e., 36 degrees Fahrenheit).

When the freezer section and refrigerator section set points are satisfied or the controller 128 has shut off the refrigeration system 62 because the temperature of the refrigerator section 40 reached the minimum refrigerator section temperature, and thus, the refrigeration system 62 is off, the controller 128 waits until the refrigerator section temperature reaches the refrigerator section set point plus the refrigerator section set point tolerance (i.e., 40 degrees Fahrenheit) or the freezer section temperature reaches 13 degrees Fahrenheit (i.e., freezer section set point plus five degrees), whichever occurs first, before turning the refrigeration system 62 back on. As long as the refrigerator section temperature is above the refrigerator section minimum temperature, the controller 128 then runs the refrigeration system 62 as described above to satisfy the refrigerator section set point and to satisfy the freezer section set point if possible.

FIG. 7 shows a decision making process 180 for controlling the temperature of the refrigeration system 62. Beginning in an off state 182 with the refrigeration system 62 off, the controller 128 determines at a decision block 184 whether the refrigerator section temperature T_(R) is above the refrigerator section minimum temperature T_(Rmin). If the refrigerator section temperature T_(R) is not above the refrigerator section minimum temperature T_(Rmin), then the refrigeration system 62 remains off and the controller remains in the off state 182. If the refrigerator section temperature T_(R) is above the refrigerator section minimum temperature T_(Rmin), then the controller 128 determines at decision block 186 whether the refrigerator section temperature T_(R) is greater than or equal to the refrigerator section set point R_(SP) plus the refrigerator section set point tolerance R_(tol) or the freezer section temperature T_(F) is greater than or equal to the freezer set point F_(SP) plus the freezer section set point tolerance F_(tol). If neither the refrigerator section temperature T_(R) is greater than or equal to the refrigerator set point R_(SP) plus the refrigerator section set point tolerance R_(to1) nor the freezer section temperature T_(F) is greater than or equal to the freezer set point F_(SP) plus the freezer section set point tolerance F_(tol), then the refrigeration system 62 remains off and the controller 126 remains in the off state 182. If either the refrigerator section temperature T_(R) is greater than or equal to the refrigerator set point R_(SP) plus the refrigerator section set point tolerance R_(tol), or the freezer section temperature T_(F) is greater than or equal to the freezer set point F_(SP) plus the freezer section set point tolerance F_(tol), then the controller 128 enters an on state 188 and turns on the refrigeration system 62.

Once in the on state 188, the controller 128 determines at decision block 190 whether the refrigerator section temperature T_(R) is greater than the refrigerator section minimum temperature T_(Rmin). If the refrigerator section temperature T_(R) is not greater than the refrigerator section minimum temperature T_(Rmin), then the controller 128 turns off the refrigeration system 62 and the controller 128 enters the off state 182. If the refrigerator section temperature T_(R) is greater than the refrigerator section minimum temperature T_(Rmin), then the controller 128 determines at decision block 192 whether the freezer section temperature T_(F) is less than or equal to the freezer set point F_(SP) minus the freezer section set point tolerance F_(tol). If the freezer section temperature T_(F) is not less than or equal to the freezer set point F_(SP) minus the freezer section set point tolerance F_(tol), then the refrigeration system 62 remains on and the controller 128 remains in the on state 188. If the freezer section temperature T_(F) is less than or equal to the freezer set point F_(SP) minus the freezer section set point tolerance F_(tol), then the controller 128 decides at decision block 194 whether the refrigerator section temperature T_(R) is less than or equal to the refrigerator set point R_(SP). If the refrigerator section temperature T_(R) is less than or equal to the refrigerator set point R_(SP), then the refrigeration system 62 is turned off and the controller 128 enters the off state 182. If the refrigerator section temperature T_(R) is not less than or equal to the refrigerator set point R_(SP), then the controller 128 decides at decision block 196 whether the refrigerator section temperature T_(R) is less than or equal to the refrigerator set point R_(SP) minus the refrigerator section set point tolerance R_(tol). If the refrigerator section temperature T_(R) is less than or equal to the refrigerator set point R_(SP) minus the refrigerator section set point tolerance R_(tol), then the refrigeration system 62 is turned off and the controller 128 enters the off state 182. If the refrigerator section temperature T_(R) is not less than or equal to the refrigerator set point R_(SP) minus the refrigerator section set point tolerance R_(tol), then the controller 128 decides at decision block 198 whether the refrigerator section temperature T_(R) is above the refrigerator section minimum temperature T_(Rmin). If the refrigerator section temperature T_(R) is not above the refrigerator section minimum temperature T_(Rmin), then the refrigeration system 62 is turned off and the controller 128 enters the off state 182. If the refrigerator section temperature T_(R) is above the refrigerator section minimum temperature T_(Rmin), then the refrigeration system 62 remains energized and the controller 128 loops through decision blocks 196 and 198 until the refrigerator section temperature T_(R) is less than or equal to the refrigerator set point R_(SP) minus the refrigerator section set point tolerance R_(tol), or the refrigerator section temperature T_(R) is not above the refrigerator section minimum temperature T_(Rmin). This loop can be interrupted by the controller 128 (e.g., a defrost cycle is required).

It should be appreciated that merely a preferred embodiment of the invention has been described above. However, many modifications and variations to the preferred embodiment will be apparent to those skilled in the art, which will be within the spirit and scope of the invention. Therefore, the invention should not be limited to the described embodiment. To ascertain the full scope of the invention, the following claims should be referenced. 

1. A combination refrigerator/freezer unit, comprising: an insulated cabinet defining a refrigerator section, a freezer section and at least one air passage between the freezer section and refrigerator section; a freezer sensor disposed in the freezer section that senses a freezer section temperature; a refrigerator sensor disposed in the refrigerator section that senses a refrigerator section temperature; a refrigeration system having a single evaporator disposed in the freezer section; and a controller for controlling operation of the refrigeration system and receiving input signals from the freezer and refrigerator sensors, the controller configured to control the refrigeration system to pass refrigerant to the evaporator in the freezer section according to at least one temperature parameter of the refrigerator section sensed by the refrigerator sensor.
 2. The combination refrigerator/freezer unit of claim 2, wherein one temperature parameter is a refrigerator section minimum temperature and the controller is configured to prevent the refrigerator section temperature from dropping below the refrigerator section minimum temperature.
 3. The combination refrigerator/freezer unit of claim 2, wherein the controller is programmed with a freezer section set point and wherein the controller is configured to energize the refrigeration system when the freezer section temperature is above the freezer section set point.
 4. The combination refrigerator/freezer unit of claim 3, wherein another temperature parameter is a refrigerator section set point, and wherein the controller is configured to energize the refrigeration system when the refrigerator section temperature is above the refrigerator section set point.
 5. The combination refrigerator/freezer unit of claim 4, wherein the controller is configured to run the refrigeration system until the freezer section temperature is below the freezer section set point and the refrigerator section temperature is below the refrigerator section set point.
 6. The cooling unit of claim 5, wherein the controller is programmed with a freezer section set point offset, and wherein the controller is configured to shut off the refrigeration system when the freezer section temperature reaches the freezer section set point minus the freezer section set point offset and the refrigerator section temperature is below the refrigerator section set point.
 7. The cooling unit of claim 5, wherein another temperature parameter is a refrigerator section set point offset, wherein the controller is programmed with a freezer section set point offset, and wherein the controller is configured to shut off the refrigeration system when the refrigerator section temperature reaches the refrigerator section set point minus the refrigerator section set point offset after the controller has detected an event when the refrigerator section temperature was not below the refrigerator section set point when the freezer section temperature reached the freezer section set point minus the freezer section set point offset.
 8. The cooling unit of claim 7, further comprising a user input connected to the controller, wherein the temperature parameters can be set by the user input.
 9. The cooling unit of claim 8, wherein the freezer section set point equals the refrigerator section set point minus a temperature set point difference.
 10. The cooling unit of claim 1, wherein the freezer and refrigerator sensors are thermistors.
 11. A combination refrigerator/freezer unit, comprising: an insulated cabinet defining a refrigerator section, a freezer section and at least one air passage between the freezer section and refrigerator section; a freezer thermistor disposed in the freezer section that senses a freezer section temperature; a refrigerator thermistor disposed in the refrigerator section that senses a refrigerator section temperature; a refrigeration system having a single evaporator disposed in the freezer section; and a controller for controlling operation of the refrigeration system and receiving input signals from the freezer and refrigerator sensors, the controller programmed with a refrigerator section minimum temperature and a refrigerator section set point; wherein the controller is configured to control the refrigeration system to energize the refrigeration system when the refrigerator section temperature is above the refrigerator section set point; wherein the controller is configured to disable the refrigeration system when the refrigerator section temperature is less than the refrigerator section minimum temperature.
 12. The combination refrigerator/freezer unit of claim 11, wherein the controller is programmed with a freezer section set point and the controller is configured to energize the refrigeration system when the refrigerator section temperature is above the refrigerator section set point.
 13. The combination refrigerator/freezer unit of claim 12, wherein the controller is configured to energize the refrigeration system until the refrigerator section temperature reaches the refrigerator section set point.
 14. A method of controlling a combination refrigerator/freezer unit with an insulated cabinet defining a refrigerator section, a freezer section, at least one air passage between the freezer section and refrigerator section, and a refrigeration system having a single evaporator disposed in the freezer section, the method comprising: sensing a freezer section temperature with a refrigerator sensor; sensing a refrigerator section temperature with a freezer sensor; and controlling the refrigeration system to pass refrigerant to the evaporator in the freezer section according to at least one temperature parameter of the refrigerator section sensed by the refrigerator sensor.
 15. The method of claim 14, wherein one temperature parameter is a refrigerator section minimum temperature, and wherein the refrigerator section temperature is prevented from dropping below the refrigerator section minimum temperature.
 16. The method of claim 15, wherein the refrigeration system is energized when the freezer section temperature is above a freezer section set point.
 17. The method of claim 16, wherein another temperature parameter is a refrigerator section set point, and wherein the refrigeration system is energized when the refrigerator section temperature is below the refrigerator section set point.
 18. The method of claim 17, wherein the refrigeration system is energized until the freezer section temperature is above the freezer section set point and the refrigerator section temperature is above the refrigerator section set point.
 19. The method of claim 15, wherein another temperature parameter is a refrigerator section set point offset and wherein the refrigeration system is energized when the freezer section temperature reaches the freezer section set point plus a freezer section set point offset, wherein the refrigeration system is energized when the refrigerator section temperature reaches the refrigerator section set point plus the refrigerator section set point offset, wherein the refrigeration system is energized until the freezer section temperature reaches the freezer section set point minus the freezer section set point offset and wherein the refrigeration system is energized until the refrigerator section temperature reaches the refrigerator section set point.
 20. The method of claim 19, wherein the refrigeration system is energized until the refrigerator section set point reaches the refrigerator section set point minus the refrigerator section set point offset after an event when the freezer section temperature had reached the freezer section set point minus the freezer section set point offset and the refrigerator section temperature had not reached the refrigerator section set point. 